In recent years, endoscopic diagnosis has easily been conducted with the spread of electronic endoscopes, and it becomes possible to infallibly find stomach cancer or large bowel cancer as initial cancers. However, as far as the diagnosis of microcarcinoma is concerned, almost the same levels of diagnostic performance are achieved by an electronic endoscope and an ordinary endoscope. The fact means that new diagnostic methods that can efficiently function electronic endoscopes have not yet been established. If microlesions can be marked with a labeling antibody that is detectable under electronic endoscopy, it may be possible to easily detect microlesions, such as those not recognizable by an ordinary endoscope, with imaging through a computerized process. However, such method has not yet been practically used.
In order to establish a method utilizing an electronic endoscope such as described above, it is necessary to directly stain a living tissue by means of an immuno-histochemical staining method. Staining methods for fixed specimens are established techniques. However, a staining method for non-fixed specimens has not yet become a technique available to those skilled in the art. For example, although an immuno-staining method for non-fixed specimens was reported [Shikoku Acta Medica, Vol. 29, No. 2, pp. 180-188, 1973], no immuno-staining method for an excised fresh specimen or a living tissue, per se, that utilizes near infrared ray has been reported in this field of the art.
In addition, a diagnostic marker that is detectable under electronic endoscopy, e.g., a labeled antibody, is also required for the aforementioned diagnostic method. Diagnostic markers are known which characterized in that a labeling compound, that emits fluorescence as ultraviolet and visible light when excited with ultraviolet rays, is bound to an antibody, and they have been commonly used for the detection of cancer cells or cancer tissues that exist in tissues isolated from living bodies. However, methods utilizing fluorescent diagnostic markers that needs excitation with ultraviolet rays cannot be applied to living bodies, because ultraviolet rays may cause damages on living tissues and DNAs. No diagnostic marker that can be directly applied to a living body has been known so far.
It is known that indocyanine green (ICG) exhibits unique absorption properties and emits fluorescence under infrared ray endoscopy. Clinical cases were reported in which indocyanine green was applied when an infrared ray endoscope was used (Gastroenterological Endoscopy, 34, pp.2287-2296, 1992; and Gastrointestinal Endoscopy, 40, pp.621-2; 628, 1994). However, in these cases, ICG was intravascularly administered. Furthermore, fluorescent dyes, including indocyanine green as a typical example, have generally high hydrophobicity and are absorbed rapidly when they, per se, are administered into intestinal tract. For this reason, attempts have been made to increase their water-solubility by introducing hydrophilic groups, e.g., sulfonyl group, into ring structures or side chain moieties, and thereby improve measurement efficiency and eliminate the problem of toxicity after absorption. However, any water-soluble labeling compound has not yet been known that can emit fluorescence comparable to that of indocyanine green.
An object of the present invention is to provide a diagnostic marker useful for directly staining a living tissue by an immuno-histochemical staining method. Another object of the present invention is to provide a diagnostic marker which emits fluorescence when irradiated with near infrared rays or far infrared rays that rarely cause histological disorders, and can be directly applied to a living body. In other word, the object of the present invention is to provide a diagnostic marker which is free from problems of damages on living tissues and DNAs due to ultraviolet excitation, and can be applied to living bodies. It is also an object of the present invention to provide a diagnostic marker which has excellent water solubility as well as the features as mentioned above.
A further object of the present invention is to provide a diagnostic marker applicable to living bodies which is useful for a quasi-internal early diagnosis of malignant neoplasms in epithelial tissues, e.g., esophagus cancer, stomach cancer, or large bowel cancer, or infectious diseases by means of an infrared endoscope or other, or useful for the identification or diagnosis of a focus in a surgical operation. A still further object of the present invention is to provide a method for directly staining a living tissue by an immuno-histochemical method using a diagnostic marker as mentioned above.